Measuring sensors are known. By determining the oxygen concentration in the exhaust gas of internal combustion engines, such measuring sensors specify the setting of a fuel-air mixture for the operation of the internal combustion engine. The fuel-air mixture can lie in the "rich" range, that is, the fuel is in stoichiometric excess, so that only a small quantity of oxygen is present in the exhaust gas in comparison to other partly unburned components. In the "lean" range, in which atmospheric oxygen predominates in the fuel-air mixture, an oxygen concentration in the exhaust gas is correspondingly high.
"Lambda probes" are known for determining the oxygen concentration in exhaust gas; these detect a lambda value &gt;1 in the lean range, a lambda value &lt;1 in the rich range, and a lambda value =1 in the stoichiometric range. A Nemst measuring cell of the measuring sensor supplies in known fashion a detection voltage, which is supplied to a circuit arrangement.
In a known design of the measuring sensor, one electrode of the Nernst measuring probe is exposed to the gas mixture (exhaust gas) being monitored, a second electrode to a reference gas. The electrodes here are arranged on opposite sides of a solid electrolyte. As a result of the oxygen concentration present in the gas mixture being measured, a difference in oxygen concentration arises between the electrodes. A constant current is passed through the Nernst measuring cell, so that a certain detection voltage is set up on the electrodes as a result of the difference in oxygen concentration present. If there is a rise or fall in the oxygen concentration in the gas mixture being measured, the detection voltage decreases or, respectively, increases.
It is known to fabricate such measuring sensors as "thick-film" planar broadband lambda probes. Here, the individual functional elements of the measuring sensor are arranged and structured in layers one atop another. This layer construction is obtained, for example, by film casting, stamping, screen printing, laminating, cutting, sintering, or a like method. It has turned out that reference gas can be consumed to various extents as a result of manufacturing-related contaminants in a reference compartment of the measuring sensor. Because, however, a consumption of reference air has a substantial effect on the detection voltage with regard to generating an accurate detection voltage during the intended use of the measuring sensor, measuring sensors fabricated by the same manufacturing steps are subject to a variation in their output signal.